Registering of a scene disintegrating into clusters with visualized clusters

ABSTRACT

A method for optically scanning and measuring a scene by a three-dimensional (3D) measurement device in which multiple scans are generated to then be registered in a joint coordinate system of the scene. At first at least one cluster is generated from at least one scan, further scans are registered for test purposes in the coordinate system of the cluster, if specified quality criteria are fulfilled and the generated clusters are then joined, for which purpose clusters are selected, registered for test purposes and registering is confirmed if appropriate, wherein the clusters to be joined are visualized with an optional possibility for the user to intervene, for supporting the selection of clusters.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of German Patent ApplicationNo. DE102014104712.5, filed on Apr. 2, 2014, the contents of which arehereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a method for optically scanning and measuring ascene using a laser scanner.

BACKGROUND OF THE INVENTION

German Published Patent Application No. DE102009015922A1 describes amethod for optically scanning and measuring a scene using a laserscanner, in which a scene is registered with multiple scans. For thispurpose, the laser scanner is taken to a new location after a scan togenerate an additional scan. The generated scans with their measuringpoints are registered in a joint coordinate system, wherein the entityof measuring points forms a three-dimensional (3D) point cloud.

Through use of known methods for registering multiple scans of a scene,the registering process, which may be based on the pairwise examinationof two scans, should theoretically be unambiguous and may take placecompletely automatically. In practice, however, for reasons ofperformance, not all scans are typically examined pairwise, but usuallyonly within a neighborhood that results, for example, from the historyof registering of the scene. This is why interruptions in theregistering process may occur.

Embodiments of the present invention are based on improving a method ofthe type mentioned hereinabove.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, at first at least onecluster is generated from at least one scan, to which further scans areadded, as long as specified quality criteria are fulfilled. Otherwise, anew cluster is generated. When auto clustering has taken place, theclusters are joined. For this purpose, the clusters and/or scans must beselected pairwise and be registered for test purposes.

The selection of the clusters and/or scans for joining the clusters cantake place in different ways. As long as the scans in their entity getsufficient information, strategies are possible which permit anautomatic joining of the clusters with a good performance, particularlyif strategies are pursued already when clustering. Cumulatively (i.e.,for additionally supporting and accelerating) or alternatively (inparticular if the information gathered from the scans is in its entitynot sufficient or if it is ambiguous), interventions by the user cantake place. In case of a post registration, these interventions can be,for example, supports in selecting the pairs, and in case of an onsiteregistration then additional scans. In all cases, confirmations by theuser can be requested after the proposed joining to a cluster.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis ofexemplary embodiments illustrated in the drawings, in which:

FIG. 1 is a schematic flow diagram of a method of automatic clustering;

FIG. 2 is a schematic representation of clusters;

FIG. 3 is a schematic representation of two scans as a split view;

FIG. 4 is a schematic flow diagram of a method of the joining of theclusters;

FIG. 5 is a schematic, partially cut representation of a laser scannerin operation, and

FIG. 6 is a perspective view of the laser scanner of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 5 and 6, embodiments of the present invention relateto a 3D coordinate measurement device which steers a beam of light to anobject O, which may either be a cooperative target such as aretroreflector or a non-cooperative target such as a diffuselyscattering surface of the object O. A distance meter in the devicemeasures a distance to the object O, and angular encoders measure theangles of rotation of two axles in the device. The measured distance andthe two angles enable a processor in the device to determine the 3Dcoordinates of the object O. Embodiments of the present inventiondisclose a laser scanner 10 as the 3D coordinate measurement device, butvarious other embodiments utilizing a laser tracker or total stationshould be clear to one of ordinary skill in the art. The 3D measurementdevice may also be a portable freestyle device with a projectorgenerating a light pattern (e.g., infrared light pattern) onto theobject O and one or more cameras capturing the light pattern on theobject O.

Laser scanners are typically used for scanning closed or open spacessuch as interior areas of buildings, industrial installations andtunnels. Laser scanners are used for many purposes, including, forexample, building information modeling (BIM), industrial analysis,accident reconstruction applications, archaeological studies, andforensics investigations. A laser scanner can be used to optically scanand measure objects in a volume around the laser scanner through theacquisition of data points representing objects within the volume. Suchdata points are obtained by transmitting a beam of light onto theobjects and collecting the reflected or scattered light to determine thedistance, two-angles (i.e., an azimuth angle and a zenith angle), andoptionally a gray-scale value. This raw scan data is collected, storedand sent to a processor or processors to generate a 3D imagerepresenting the scanned area or object. To generate the image, at leastthree values are collected for each data point. These three values mayinclude the distance and two angles, or may be transformed values, suchas x, y, z coordinates.

In FIGS. 5 and 6, a laser scanner 10 is shown for optically scanning andmeasuring the environment surrounding the laser scanner 10. The laserscanner 10 comprises a measuring head 12 and a base 14. The measuringhead 12 is mounted on the base 14 such that the measuring head 12 canrotate with respect to the base 14 about a first axis 12 a, driven by afirst rotary drive. The rotation about the first axis 12 a may be aboutthe center of the base 14. The measuring head 12 comprises a mirror 16,which can rotate about a second axis 16 a, driven by a second rotarydrive. Referring to a normal upright position of the laser 10, the firstaxis 12 a may be called the vertical axis or azimuth axis, while thesecond axis 16 a may be called the horizontal axis or zenith axis. Thelaser scanner 10 may comprise a gimbal point or center C₁₀ that is theintersection point of the first axis 12 a and the second axis 16 a.

The measuring head 12 is further provided with an electromagneticradiation emitter, such as light emitter 17, for example, that emits anemission light beam 18. In an embodiment, the emission light beam 18 isa coherent light such as a laser beam. The laser beam may have awavelength range of approximately 300 to 1600 nanometers, for example790 nanometers, 905 nanometers, 1550 nanometers, or less than 400nanometers. It should be appreciated that other electromagneticradiation beams having greater or smaller wavelengths may also be used.The emission light beam 18 may be amplitude or intensity modulated, forexample, with a sinusoidal waveform or with a rectangular waveform.Alternatively, the emission light beam 18 may be otherwise modulated,for example, with a chirp signal, or coherent receiver methods may beused. In the present embodiment, the emission light beam 18 is acontinuous wave laser beam. However, it may also be a pulsed laser. Theemission light beam 18 is emitted by the light emitter 17 onto themirror 16, where it is deflected to the environment of the laser scanner10.

A reflected light beam, hereinafter called a reception light beam 20, isreflected from the environment by an object O. The reflected orscattered light is intercepted by the rotary mirror 16 and directed ontoa light receiver 21 with reception optics. The directions of theemission light beam 18 and the reception light beam 20 result from theangular positions of the measuring head 12 and the mirror 16 about theaxes 12 a and 16 a, respectively. These angular positions in turn dependon the corresponding rotary drives. The angle of rotation about thefirst axis 12 a is measured by a first angular encoder. The angle ofrotation about the second axis 16 a is measured by a second angularencoder.

A control and evaluation unit 22 has a data connection with the lightemitter 17 and the light receiver 21 inside the measuring head 12,whereby parts of the control and evaluation unit 22 can be arranged alsooutside the measuring head 12, for example as a computer connected tothe base 14. The control and evaluation unit 22 is configured todetermine, for a multitude of measuring points X, a corresponding numberof distances d between the laser scanner 10 and the measuring points Xon object O. The distance to a particular measuring point X isdetermined based at least in part on the speed of light in air throughwhich electromagnetic radiation propagates from the device 10 to themeasuring point X. In an embodiment, the phase shift in the modulatedlight beam 18, 20, sent to the measuring point X and received from it,is determined and evaluated to obtain a measured distance d.

The speed of light in air depends on the properties of the air such asthe air temperature, barometric pressure, relative humidity, andconcentration of carbon dioxide. Such air properties influence the indexof refraction of the air. The speed of light in air is equal to thespeed of light in vacuum divided by the index of refraction. A laserscanner of the type discussed herein is based on the time-of-flight ofthe light in the air (the round-trip time for the light to travel fromthe device to the object and back to the device). A method of measuringdistance based on the time-of-flight of light (or the time-of-flight ofany type of electromagnetic radiation) depends on the speed of light inair and is therefore easily distinguished from methods of measuringdistance based on triangulation. Triangulation-based methods involveprojecting light from a light source along a particular direction andthen intercepting the light on a camera pixel along a particulardirection. By knowing the distance between the camera and the projectorand by matching a projected angle with a received angle, the method oftriangulation enables the distance to the object to be determined basedon known length and two known angles of a triangle. The method oftriangulation, therefore, does not directly depend on the speed of lightin air.

The measuring head 12 may include a display device 24 integrated intothe laser scanner 10. The display device 24 includes a user interface,which may be a graphical touch screen, as shown in FIG. 6. For example,the display device 24 may have a user interface that allows the operatorto provide measurement instructions to the laser scanner 10, inparticular to set the parameters or initiate the operation of the laserscanner 10, and the display device 24 may also display measurementresults.

In an embodiment, the scanning of the environment of the laser scanner10 takes place by rotating the mirror 16 relatively quickly about thesecond axis 16 a while rotating the measuring head 12 relatively slowlyabout the first axis 12 a, thereby moving the assembly in a spiralpattern. In an exemplary embodiment, the rotary mirror 16 rotates at amaximum speed of 5820 revolutions per minute. A scan is defined to bethe entity of measuring points X in such a measuring. For such a scan,the center C₁₀ defines the origin of the local stationary referencesystem. The base 14 rests in this local stationary reference system.

In addition to measuring a distance d from the center C₁₀ to a measuringpoint X on the object O, the laser scanner 10 may also collectgray-scale values related to the received optical power. The gray-scalevalue may be determined, for example, by integration of thebandpass-filtered and amplified signal in the light receiver 21 over ameasuring period attributed to the measuring point X. Optionally, colorimages can be generated by a color camera 25. Through use of these colorimages, colors (R, G, B) can be assigned to the measuring points X asadditional values.

To scan a scene from different directions or a large space, multiplescans are captured from different locations (corresponding to an amountof different centers) and then registered in a joint coordinate systemXYZ of the scene. The laser scanner 10 must change its location for thispurpose, thus moving each time the center C₁₀ of the laser scanner 10within the joint coordinate system XYZ to a new center from the amount.

For registering the scans, point-based methods or methods using targetscan be used. In an exemplary embodiment, registering is performedthrough use of targets. The targets are localized and identified inoverlapping areas of the scans. Both, “natural” targets, i.e., certainformations of the object O, and “artificial” targets, i.e., targetswhich have been applied especially for the scanning process to theobject O or to the environment, for example checker-board patterns, areappropriate as targets. The geometry in which a target is embedded andwhich is defined by the adjacent targets, is determined for each target,for example as described in the aforementioned German Published PatentApplication No. DE102009015922A1. The embedding geometries can then becompared with each other to first automatically find corresponding pairsof targets and then find the best possible assignment of the two scans.When all scans are registered in the joint coordinate system XYZ, theentity of all measuring points X of all scans forms a three-dimensionalpoint cloud 3DP.

It is usually possible to register all scans through use of the targets,even without having additional information on the relative positions ofthe centers of the scans. To improve performance, the time stamp of thescans can be used to find and register adjacent scans faster. The resultof registering can be shown on the display unit 24. A confirmation bythe user is optional.

It is, however, also possible that problems occur during registering,for example not enough targets in overlapping areas of the scans,ambiguous, embedding geometries or a difficult topology. It is alsopossible that problems are present which are not recognized immediately,but only by the user. Therefore, auto clusters can be generated whichcomprise unambiguously matching scans. For defining such unambiguousmatching, specified quality criteria can be defined which must befulfilled. Such a quality criterion can be, for example, a thresholdvalue for the remaining inverse squares of the targets, after theembedding geometries have been assigned, wherein the quality criterionshall increase with increasing concordance.

In FIG. 1, a schematic representation of the procedure during“auto-clustering” shows how it can be automatically carried out, forexample, through use of a suitable filtering device. After an initialstep 101, a first cluster G_(l) is defined in a processing step 102, andthe first scan {X⁽¹⁾}—initially as the only scan—is assigned to it(shown by an arrow). This first scan {X⁽¹⁾} also defines the coordinatesystem of the first cluster G_(l). For a following loop which processesa cluster G_(m) during every cycle, therefore, during the first cycle,m=1. The further scans {X^((i))} start with i=2.

The loop then starts, the loop containing a processing step 103 in whicha further scan {X^((i))} is registered for test purposes in thecoordinate system of the cluster G_(m) which is processed at present.The cluster G_(m) can contain a relatively large quantity of targets.There are two possibilities. Either, for reasons of performance, a pairis formed, for example, from the last successfully registered scan (oranother scan) of the cluster G_(m) and the further scan {X^((i))}. Or,for reasons of improved success in registering, the pair is formed fromthe cluster G_(m) (complete cluster G_(m) or peripheral portion composedof several scans) and the further scan {X^((i))}. The expression“peripheral portion” should paraphrase that the cluster G_(m) iscomposed of many scans overlapping with their respective neighbors, andit is rather probable that a further scan {X^((i))} is not overlappingwith registered scans in the center of the cluster G_(m) but with(several) registered scans in the periphery of the cluster G_(m),wherein the common targets in the overlapping parts of the scans areused for registering the scans. In particular, the number of commontargets in the peripheral portion of the cluster G_(m), formed ofseveral scans, is larger than the number of targets of a single scan ofthe cluster G_(m), thus increasing the probability for a success inregistering the further scans {X^((i))}. The pair is registered for testpurposes.

A decision process 104 checks whether registering has been successful,i.e., whether the quality criteria for registering are fulfilled. Ifthis is the case (Y), registering is confirmed (by the procedure) in aprocessing step 105, otherwise (N), registering for test purposes isrejected.

A subsequent decision step 106 checks whether further scans {X^((i))}are available, which have not yet been registered for test purposes inthis loop (“free scans”). Such a check usually will take place by anincrementing loop counter (e.g., number “I” of the scan) and ofappropriate flags. If such free scans {X^((i))} are still available (Y),the loop jumps back to processing step 103 with registering for testpurposes. The decision step 106 could take place also at the beginningof the loop. If no free scans {X^((i))} are available any longer,auto-clustering ends with a final step 107.

If registering for test purposes is rejected after the decision step104, a new cluster G_(m) (with m=m+1) is defined in a processing step108, and the last scan {X^((i))} registered for test purposes, isassigned to this new cluster G_(m). This last-named scan {X^((i))}defines the coordinate system of the new cluster G_(m). The procedure isthen continued with processing step 103 of the registering for testpurposes.

In a modified embodiment, a new cluster is not immediately started incase of an unsuccessful registering for test purposes, but a specifiednumber of the next free scans {X^((i))} is tested instead for assigningto the present cluster G_(m). With a view to performance, it isappropriate to limit the number of these scans still to be tested, bydefining a limit, for example by the time stamp or the continuous numberof the scan, i.e., a limit with respect to space and/or time, so that itis only tried to register scans which are adjacent with respect to time(and consequently usually also with respect to space) for test purposes.This reduces time consumption or the complexity of registering.

In an alternative to the described serial procedure, the scans {X^((i))}can be tested pairwise, in a more parallel method (corresponding to thecrystal growth), for registering for test purposes. From each matchingpair, a cluster G_(m) is formed as a nucleation site. From the clustersG_(m) or from single scans from the clusters G_(m) and the free scans{X^((i))}, new pairs arise, which again are checked for being registeredfor test purposes, until, in the end, no further registering issuccessful.

In the case of a building, the clusters G_(m) frequently compriseadjacent scans {X^((i))} of the same room, the same floor, the samebuilding or from its interior and exterior.

The problem remains to join the clusters G_(m), for example on anappropriate registering device. It must thereby be taken into account(as in processing step 103) that the clusters G_(m) contain a relativelylarge amount of targets. For reasons of performance, when forming thepairs, single scans {X^((i))} may be selected from the clusters G_(m).However, for increasing the success of registering for test purposes,and in particular if pairs of single scans {X^((i))} were used in step103, it is better to use whole clusters G_(m) or peripheral portionsthereof. Either a single scan {X^((i))} is selected from a first clusterG_(m), and the second cluster G_(l) is used as a whole or in aperipheral portion. Or the pairs are formed by two clusters G_(m), G_(l)and/or peripheral portions thereof. Such a scan {X^((i))} selected froma first cluster G_(k), is then registered (for test purposes), forexample, in the coordinate system of a second cluster G_(l). Joining ofthe clusters G_(m) can be visualized, for example to show the progressor to get an optional confirmation of the user or to request an optionalsupport by the user.

A possible first visualization (“correspondence view”) is the compressedrepresentation of all clusters G_(m), side by side, for example on thedisplay unit 24. The expression “side by side” means a spatial adjacentarrangement of the clusters G_(m) on the display without penetration oroverlap of the clusters G_(m). The visualization tries to use structuresand features of the clusters G_(m) which help the user to recognize theclusters G_(m). In the case of a building, it is appropriate to select atop view of the clusters G_(m), corresponding to a floor plan of thebuilding. In FIG. 2 this is shown in an exemplary manner with threeclusters G_(k), G_(l) and G_(m), wherein the continuous lines aresupposed to represent recognized walls and broken lines the approximateextension of the three-dimensional point cloud 3DP. Updatedvisualizations show the progress when joining the clusters. That is,once two clusters G_(m) have been joined, they are visualized in thisjoined state on the display. Every pair of joined clusters G_(m) is apartial success. It should be noted that in special cases, e.g., if acluster G_(m) extends on two floors of the building, it may helpful toform sub-clusters of said G_(m), e.g., one sub-cluster in each floor.Each of these sub-clusters may then be displayed side by side with theother clusters G_(m) of the same floor. Selecting one of the floors, theuser may have a top view on all clusters G_(m) of the selected floor.

A possible second visualization (“split view”) is the representation ofthe pair of clusters G_(k), G_(l) (which are processed at the moment) orof selected scans {X^((i))}, {X^((j))} from the clusters G_(k), G_(l),in a split (screen) view, as shown in FIG. 3. This representation of thetwo scans {X^((i))}, {X^((j))} with their targets T^((i)) ₁, T^((i)) ₂,T^((i)) ₃, T^((i)) ₄ and T^((i)) ₁, T^((i)) ₂, T^((i)) ₃, T^((i)) ₄ isschematic, since the assumed relative rotation would be unproblematic inreality. Both visualizations can also be combined in such a way that achange between them is possible.

Joining of the clusters G_(m) with optional visualization is shown as aflow chart in FIG. 4. After an initial step 111 the above-describedvisualization takes place in an optional output step 112. In asubprogram 113 which is invoked (and described later), two clusters andeach one scan from each of the two clusters are selected, which togetherbuild a pair to be registered for test purposes. More precisely, a scan{X^((i))} is selected from a first cluster G_(k), such scan beingsupposed to be registered for test purposes in the coordinate system ofa second cluster G_(l), for which, in turn, a scan {X^((j))} is selectedrepresentatively from this second cluster G_(l), and the two scans{X^((i))}, {X^((j))} form the pair.

In a processing step 114 it is tried to register the pair for testpurposes—as in processing step 103—and to thus join the clusters. In adecision step 115 it is checked whether such joining has beensuccessful. If this is the case (Y), registering is confirmed in aprocessing step 116 (corresponding to processing step 105), andoptionally a new output step 117, corresponding to output step 112 takesplace. Otherwise (N) the two clusters remain separate. In a furtherdecision step 118 (which can be arranged also at another point of theloop) it is checked, whether there are still clusters G_(m) available,which have not yet been joined, i.e. which are still “free.” If this isthe case (Y), the loop continues, invoking the subprogram 113, andadding a processing step 119. Otherwise (N) all clusters G_(m) arejoined, so that it is possible to finish with a final step 120. Theoptional, added processing step 118, which can be carried out also atthe beginning of the loop, changes parameters, if all free clusters havealready been tested unsuccessfully with a view to joining. Inparticular, the quality criteria for registering the scans for testpurposes can be reduced.

The subprogram 113 with the selection and formation of the pairs can beimplemented in different, modified ways.

A first possibility is to strategically select the clusters G_(k), G_(i)and/or the scans {X^((i))}, {X^((j))} for forming the pairs. If twoclusters G_(k), G_(l), which are consecutive regarding their time stampare selected, then multiple scans {X^((i))} from a first cluster G_(k)can be selected consecutively (e.g., each time the subprogram 113 isinvoked) to form pairs with the first scan {X^((j))} of the secondcluster G_(l) which is later—with a view to the time stamp. Ifappropriate, only the last scan {X^((i))} is selected from the firstcluster G_(k). Again, the first cluster G_(k) and the second clusterG_(l) may be selected as a whole or peripheral regions of the twoclusters G_(k), G_(l) may be selected. Or the pair is formed by thewhole (or peripheral portion of the) first cluster G_(k) on one hand andthe first scan {X^((j))} of the second cluster G_(l) on the other hand.It then proceeds on the assumption that the first cluster G_(k) willcome to a dead end and that the second cluster G_(i) branches at anearlier point which, due to the defined limit with respect to spaceand/or time in decision step 106, has not yet been checked. Within thestrategy, the limit is repealed. Further strategies are possible. Incase of a building, a further strategy may be to distinguish clustersG_(k), G_(l) by floors. The floors may be detected by an altimeter,e.g., being a built-in sensor of the 3D measurement device.

Since some of the pairs have already been tested unsuccessfully once(which is appropriate to be noted), the processing step 118 with themodified parameters can be helpful. Such implementation of thesubprogram 113 (with strategic selection) provides a completelyautomatic method for selecting the clusters G_(k), G_(l) and the scans{X^((i))}, {X^((j))}. Modifying the parameters may comprise a reductionof the quality criteria. As subprogram 113 is inside a loop, thereduction will be iterative. With reduced quality criteria, a finalconfirmation by the user becomes appropriate, however.

A second possibility is to assume a support by the user in subprogram113, i.e., a semi-automatic method for joining the clusters G_(m).

In the case of the first visualization with the clusters side by side(FIG. 2), the user can shift the clusters relative to each other by anappropriate input unit, for example a mouse. The user shifts, forexample cluster G_(l) to cluster G_(k), so that the point cloudsoverlap. With the information gained from the input and output units,the concerned cluster G_(k) and cluster G_(l) can be set in a spatialrelationship to each other, and the appropriate scans can be selectedtherefrom. Since the corresponding targets are in immediate vicinity toeach other, registering for test purposes in processing step 114 willthen soon be successful.

In the case of the second visualization in a split view, FIG. 3 showsthe two scans on the left and on the right. The targets T^((i)) ₁,T^((i)) ₂, T^((i)) ₃, T^((i)) ₄ of the scan represented on the left{X^((i))} are supposed to correspond with the targets T^((i)) ₁, T^((i))₂, T^((i)) ₃, T^((i)) ₄ of the scan {X^((j))} represented on the right.The user can provide for this correspondence by an appropriate inputunit, for example a mouse or a touchscreen. At first it is tried tocarry out registering for test purposes with two pairs of suchcorresponding targets, for example T^((i)) ₁ and T^((i)) ₁ as well asT^((i)) ₂ and T^((i)) ₂ in processing step 114. With each furtherinvoking of subprogram 113, a further pair of corresponding targetswould be called.

A third possibility exists in the case of an onsite registration. Forthis purpose, the scans {X^((i))} are registered, i.e., joined to acluster, already while the scene is still being registered (i.e. scannedand measured optically), i.e., as long as the user with laser scanner 10is still on site. Registering may take place between two scans when thecolor camera 25 is used. Optionally, the laser scanner 10 allows for thenext (regular) scan {X^((i))} only when a registering of the scans madeuntil now has been successful.

If the previous cluster shall be terminated and a new cluster isstarted, i.e., if registering for test purpose has been unsuccessful,subprogram 113 can request the user to generate at least one additional(extraordinary) scan {X^((j))}, usually in the area scanned last, fromwhich the cluster which has just been terminated and the cluster whichhas been started (i.e., the unsuccessfully joined clusters) come, andwhich can be visualized to the user in a contemporary way. The later thecall for the additional scan {X^((j))} takes place, the more difficultis it for the user to find the correct area with the unsuccessfullyjoined clusters.

The pairs are formed from the additional scan {X^((j))} and fromselected, available scans {X^((i))} of the cluster which has just beenterminated. Selection can again take place strategically (andautomatically), as in the first possibility of implementing subprogram113. When the terminated cluster has been successfully complemented withthe additional scan, it is tried to join the terminated cluster and thecluster which has just been started. If appropriate, a further call foran additional scan takes place.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A method for optically scanning and measuring ascene by a three-dimensional (3D) measurement device in which multiplescans are generated by the device, and the multiple scans are thenregistered in a joint coordinate system of the scene, comprising:generating at least one cluster from at least one scan of the multipleof scans; registering additional scans from the multiple of scans fortest purposes in a coordinate system of the generated at least onecluster; confirming the registering of the additional scans if specifiedquality criteria are fulfilled; and joining clusters generated from theadditional scans by selecting at least two clusters and registering theat least two clusters for test purposes and confirming the registering,wherein the clusters to be joined are visualized for supporting userselection of the at least two clusters.
 2. The method of claim 1,wherein the clusters to be joined are visualized side by side in acompressed representation of all clusters.
 3. The method of claim 1,wherein progress of joining the clusters is shown.
 4. The method ofclaim 1, wherein the selected at least two clusters are shifted relativeto each other.
 5. The method of claim 4, wherein the selected at leasttwo clusters are shifted relative to each other such that point cloudsassociated with each of the at least two clusters overlap.
 6. The methodof claim 5, wherein the selected at least two clusters which have beenshifted relative to each other are set in spatial relationship to eachother with information gained from input and output units, and thatscans are selected from the selected at least two clusters to form pairsof selected scans.
 7. The method of claim 6, wherein the pairs ofselected scans are registered for test purposes and registering isconfirmed is specified quality criteria are fulfilled.
 8. The method ofclaim 1, wherein automatic registering for test purposes use targets inoverlapping areas of the scans or point-based methods.
 9. A 3Dmeasurement device for carrying out the method of claim 1, comprising acontrol and evaluation unit which determines, for a plurality ofmeasuring points of every one of the scans at least a distance from thea center of the 3D measurement device to the object and registers thegenerated scans in a joint coordinate system of the scene.
 10. The 3Dmeasurement device of claim 9, configured as a laser scanner comprisinga base, a measuring head which is rotatable with regard to the base, alight emitter which emits an emission light beam, a light receiver whichreceives a reception light beam which is reflected by an object in theenvironment of the laser scanner or scattered otherwise, wherein thecenter of the laser scanner rests while a scan is made and is movablebetween the scans.
 11. The 3D measurement device of claim 9, furthercomprising a display unit for visualizing the clusters to be joined.